This invention relates to equipment and the corresponding method for constructing concrete micropiles of the type used for soil consolidation, underpinning and the like, or for the anchorage of tie-rods, especially active anchors.
The equipment according to the invention includes a disposable drilling rod fitted at the tip with a bit equipped with two or more nozzles for the injection of a liquid at high pressure; and means designed to pull a tubular protective element, not adhering to the drilling rod, together with said rod during drilling.
In detail, the invention involves fitting to the drilling rod a conical sleeve with one threaded end for connection to the tubular protective element, which said conical sleeve is fitted to the rod in such a way that it can rotate, stop means which prevent it from traversing being fitted, so that the drilling rod can rotate freely and pull said sleeve into the ground during drilling.
The invention also relates to a method of constructing micropiles which involves drilling with a disposable drilling rod that pulls a protective tube, which does not adhere to the drilling rod, with said rod during drilling; when the area of stable soil is reached, drilling continues, and a mixture of water and cement is simultaneously injected into the soil while the drilling rod descends and rotates; after drilling, the proximal end of the drilling rod is anchored to a plate and traction is applied if necessary.
The method according to the invention not only enables micropiles to be constructed in a short time, with a considerable saving on the cost of the finished product, but also allows the construction of active anchors, namely tie-rods to which traction can be applied after they have been laid. One of the most effective methods of stabilising soil or slopes, or increasing the load-bearing capacity of soil, is the construction of micropiles, a technique that involves making reinforced concrete piles of suitable size in the soil in order to stabilise the soil and increase its ability to bear loads.
In accordance with known techniques, these piles are constructed by drilling a hole in the ground with a drilling rod fitted with a bit at the tip, inserting steel reinforcement in the hole, and filling it with concrete.
This is a rather laborious technique, which involves long working times and correspondingly high costs.
In recent years a new technique has been developed, described in European patent application no. 1,719,841 by the same applicant, which involves drilling with a rod that acts as reinforcement for the pile and injecting grout directly during drilling; this means injecting downwards from the surface, unlike the earlier methods, in which the grouting stage was performed upwards, from the bottom of the hole to the surface.